1. Field of the Invention
The present invention is broadly concerned with an improved railroad train braking system for braking railroad cars which have been isolated from the braking control of the engineer. More particularly, it is concerned with a braking system in which a safety apparatus continuously discharges a small amount of pressurized air at a predetermined rate from the brake pipe of the last car of a train in order to set the brakes on a rearward portion of a train which has been isolated from control and make-up air of the locomotive.
2. Description of the Prior Art
Prior art railroad train braking systems include a source of compressed air located in the locomotive of the train controlled by a brake valve operable by the engineer for supplying and controlling air pressure conveyed by brake pipes extending along the lengths of the cars of the train. Two valves known as angle cocks are coupled with respective ends of the brake pipe of each car and flexible brake hoses intercouple the brake pipes of adjacent cars to form a continuous air conduit from the locomotive through the length of the train. When a caboose is not included as the last car in the train, an end-of-train device is coupled with the terminal brake hose of the last car which provides air pressure telemetry. This device senses the air pressure in the brake pipe of the last car and transmits a radio signal representative of the pressure to a receiver in the locomotive. In this way, the engineer can monitor the air pressure at the terminal end of the train.
As part of the braking system, each car also includes a reservoir which stores pressurized air for operating a brake cylinder which in turn operates to set or release the brake shoes of the car. The reservoir is divided into auxiliary and emergency compartments for providing pressurized air used in normal and emergency operations. The reservoir is charged with compressed air from the brake pipe through an air distribution control valve typically known as an "A/B valve." This valve also controls the application of air from the reservoir to the brake cylinder in response to brake pipe pressure signals initiated by the brake valve in the locomotive. In the past, it was normal for air leaks to exist in the train braking system especially at the "glad hand" couplers of the air hoses. In today's trains, however, air leaks are minimal. Nevertheless, the compressed air source in the locomotive is still available to provide make-up air as needed.
In order to brake the train, the engineer operates the brake valve in the locomotive which reduces the brake pressure in the brake pipes of the cars. This pressure reduction operates as an air signal to the A/B valves in each car. In response, the A/B valves release air from the reservoirs to the brake cylinders which applies the brakes on each car. When the engineer moves the brake valve to the released position, brake pipe pressure increases which signals the A/B valves to shift the brake cylinders to the released position. The reservoirs are then recharged with air from the brake pipe.
Emergency braking occurs upon a substantial reduction in brake pipe pressure, either because the engineer has moved the brake valve to the emergency position or because a break in the train has occurred. This reduction in pressure is sensed by the A/B valve in each car which then applies air from both auxiliary and emergency compartments to the brake cylinders causing full force application of the brake shoes against the wheels of the train.
The prior art train braking system discussed above presents a serious inherent problem. When a train is stopped at a crossing, for example, vandals have been known to close one or more of the angle cocks. When such occurs, the brake pipes of those cars downstream of the closed angle cock are isolated from the brake control in the locomotive. Furthermore, the air pressure in the isolated brake pipes is sealed therein which maintains the brakes of these cars in the released position. Moreover, the telemetry unit at the rear of the train is also isolated and cannot signal the locomotive that a problem exists. When the engineer next attempts to brake the train by reducing brake pipe pressure, only those cars forward of the closed cock receive the braking signal and the braking action of these forward cars may be insufficient to stop the train. In the past, this has resulted in "run away" trains and serious accidents. Even if the braking force is sufficient to stop the train, "run in" of the unbraked rearward cars into the forward cars occurs upon application of the brakes with possible car derailment.